An IP Multimedia Subsystem (hereinafter IMS) enables an operator of a Public Land Mobile Network (hereinafter PLMN) to offer their subscribers multimedia services based on and built upon Internet applications, services and protocols. These multimedia services may be particularly accessible via IMS applications.
A complete solution for the support of IMS applications, in accordance with 3GPP IMS-related technical specifications, includes terminals for the subscribers or users of the IMS, one or more IP-Connectivity Access Network (hereinafter IP-CAN), and specific functional elements of the IMS as described in 3GPP TS 23.228: “IP Multimedia Subsystem; Stage 2”. An exemplary IP-CAN may be a GPRS core network with a GERAN and/or UTRAN radio access networks. Ongoing 3GPP Release 8 also covers a so-called SAE network as a new type of IP-CAN, in accordance with 3GPP TS 23.401.
Different services and applications can be offered on top of IMS. The IMS allows deployment of peer-to-peer applications such as Multimedia Telephony, Push-to-Talk over Cellular, real-time video sharing, etc, for which the transport connections are dynamically negotiated by a protocol exchange between two end-points. Such protocol exchange is conventionally carried out by coupled protocols such as the Session Initiation Protocol (hereinafter SIP) and the Session Description Protocol (hereinafter SDP) may be, namely a SIP/SDP exchange.
In order to provide a satisfactory and reliable service experience, operators need to take special care of the quality, effective charging and potential fraud on the use of services and IMS applications. To this end, a Policy and Charging Control (hereinafter PCC) architecture is provided, as disclosed in 3GPP TS 23.203, to help operators on the control of the above issues. Thus, the PCC architecture cooperates with the IMS in order to provide a selective control of IP flows, such as QoS, firewall, multiplexing, etc, as well as a selective handling of the negotiated IP flows.
This PCC architecture generally includes an Application Function (hereinafter AF) offering applications that require policy and charging control of resources in the bearer plane and wherein service characteristics are negotiated through in the signalling plane; a Policy and Charging Enforcement Function (hereinafter PCEF) providing service data flow detection, charging and policing enforcement over the traffic in the bearer plane and wherein the service is actually provided through; and a Policy and Charging Rules Function (hereinafter PCRF) providing control functions and installing rules at the PCEF to ensure that only authorized media flows are allowed and are applied the right QoS through the right bearer.
At present, the establishment of bearers can be initiated and managed by the network (hereinafter NW) or by the user equipment (hereinafter UE) via so-called NW-initiated or UE-initiated Bearer Control Procedures. In this respect, the present invention is originally aimed for UE-initiated Bearer Control Procedures, though its teaching may solve similar issues turning up in NW-initiated Bearer Control Procedures.
A conventional scenario may be where a user with a UE accesses the IMS through a Proxy Call Session Control Function (hereinafter P-CSCF) and gets IP connectivity via an IP-CAN such as GPRS. Where this scenario includes a PCC architecture, the AF is included in, or in close cooperation with, the P-CSCF; the PCEF may be included in, or in close cooperation with, a Gateway GPRS Support Node (hereinafter GGSN), a Packet Data Network Gateway (hereinafter PDN-GW), or any other network node depending on the selected IP-CAN; and the PCRF may be provided as a separate server logically located between the signalling plane and the bearer plane, or be integrated with the P-CSCF or the GGSN, or with any other network node.
In a traditional scenario, where the PCC architecture is used, a sequence for establishing an IMS session starts when the UE of an originating user submits a SIP Invite message including an SDP offer towards an originating P-CSCF acting as the entry to the IMS. This SDP offer is transmitted through IMS Core nodes, that is, those IMS entities of the originating and/or destination IMS network that, for the purpose of the present invention, are not essential for the understanding of the proposed solution. Upon receipt of a corresponding SDP answer to the originating offer after having negotiated the media, the P-CSCF, or rather the AF included therein, submits a corresponding QoS authorization towards the PCRF, whilst the P-CSCF forwards the received SDP answer towards the UE of the originating user, that is, the originating UE for the sake of simplicity. Afterwards, in a UE-init Bearer Control mode, the originating UE initiates the reservation of QoS resources, namely a so-called bearer request throughout the present specification, towards the PCC architecture, namely towards the PCEF which asks the PCRF for applicable control rules. In the current situation, the QoS authorization always reaches the PCRF before having been asked for applicable control rules for the bearer.
However, the 3GPP TS 23.228 states for Multimedia Telephony that, if provided with the appropriate rules, the reservation of bearer resources may be initiated by the UE during the initial SIP Invite request. In this situation, the PCRF receives a request to install control rules before having received any QoS Authorization from the P-CSCF, so that such request is rejected in a conventional PCC architecture.